The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The present application relates to the treatment of subterranean formations. More particularly, the present application relates to compositions and methods utilizing CO2 activated swellable elastomers in acidizing or matrix stimulation.
Hydrocarbons (oil, natural gas, etc.) are typically obtained from a subterranean geologic formation (i.e., a “reservoir”) by drilling a well that penetrates the hydrocarbon-bearing formation. In order for hydrocarbons to be “produced”, that is, travel from the formation to the wellbore (and ultimately to the surface), there must be a sufficiently unimpeded flowpath from the formation to the wellbore. This flowpath is through the formation rock, e.g., solid carbonates or sandstones having pores of sufficient size, connectivity, and number to provide a conduit for the hydrocarbon to move through the formation.
In order to achieve sufficient production, hydrocarbon wells (e.g., oil wells) are often treated by removing (by dissolution) near-wellbore formation damage or by creating alternate flowpaths by fracturing or dissolving small portions of the formation at the fracture face. These variants of a stimulation operation are known as “matrix treatment”, “acidizing,” and “acid fracturing”, respectively. Generally speaking, acids, or acid-based fluids, are useful for these stimulation operations due to their ability to dissolve both formation minerals (e.g., calcium carbonate) and contaminants (e.g., drilling fluid coating the wellbore or penetrated into the formation) introduced into the wellbore/formation during drilling or remedial operations. Conductive flow channels called wormholes are also formed, which extend approximately radially from the wellbore.
However, when acid is pumped into a subterranean formation, the acid flows preferentially into the highest solubility or the highest permeability regions, such as large pores, vugs or natural fractures. Acid reaction in the high-solubility or high-permeability region would leave the low permeability region substantially untreated. This is less desirable because the high permeability region already has high conductivity, and the low permeability region is more in need of the treatment. Moreover, acid that enters vugs or natural fractures may be substantially wasted.
There is a need for a fluid that can automatically plug the high permeability region and divert to the low permeability region.